#include <stdio.h>
#include <stdlib.h>
#include <uv.h>
#include <curl/curl.h>

uv_loop_t* loop;
CURLM* curl_handle;
uv_timer_t timeout;

typedef struct curl_context_s
{
    uv_poll_t poll_handle;
    curl_socket_t sockfd;
} curl_context_t;

static curl_context_t* create_curl_context(curl_socket_t sockfd)
{
    curl_context_t* context;

    context = (curl_context_t*)malloc(sizeof(*context));

    context->sockfd = sockfd;

    uv_poll_init_socket(loop, &context->poll_handle, sockfd);
    context->poll_handle.data = context;

    return context;
}

static void curl_close_cb(uv_handle_t* handle)
{
    curl_context_t* context = (curl_context_t*)handle->data;
    free(context);
}

static void destroy_curl_context(curl_context_t* context)
{
    uv_close((uv_handle_t*)&context->poll_handle, curl_close_cb);
}

static void add_download(const char* url, int num)
{
    char filename[50];
    FILE* file;
    CURL* handle;

    snprintf(filename, 50, "%d.download", num);

    file = fopen(filename, "wb");
    if (!file)
    {
        fprintf(stderr, "Error opening %s\n", filename);
        return;
    }

    handle = curl_easy_init();
    curl_easy_setopt(handle, CURLOPT_WRITEDATA, file);
    curl_easy_setopt(handle, CURLOPT_PRIVATE, file);
    curl_easy_setopt(handle, CURLOPT_URL, url);
    curl_multi_add_handle(curl_handle, handle);
    fprintf(stderr, "Added download %s -> %s\n", url, filename);
}

static void check_multi_info(void)
{
    char* done_url;
    CURLMsg* message;
    int pending;
    CURL* easy_handle;
    FILE* file;

    while ((message = curl_multi_info_read(curl_handle, &pending)))
    {
        switch (message->msg)
        {
        case CURLMSG_DONE:
            /* Do not use message data after calling curl_multi_remove_handle() and
               curl_easy_cleanup(). As per curl_multi_info_read() docs:
               "WARNING: The data the returned pointer points to will not survive
               calling curl_multi_cleanup, curl_multi_remove_handle or
               curl_easy_cleanup." */
            easy_handle = message->easy_handle;

            curl_easy_getinfo(easy_handle, CURLINFO_EFFECTIVE_URL, &done_url);
            curl_easy_getinfo(easy_handle, CURLINFO_PRIVATE, &file);
            printf("%s DONE\n", done_url);

            curl_multi_remove_handle(curl_handle, easy_handle);
            curl_easy_cleanup(easy_handle);
            if (file)
            {
                fclose(file);
            }
            break;

        default:
            fprintf(stderr, "CURLMSG default\n");
            break;
        }
    }
}

static void curl_perform(uv_poll_t* req, int status, int events)
{
    int running_handles;
    int flags = 0;
    curl_context_t* context;

    if (events & UV_READABLE)
        flags |= CURL_CSELECT_IN;
    if (events & UV_WRITABLE)
        flags |= CURL_CSELECT_OUT;

    context = (curl_context_t*)req->data;

    curl_multi_socket_action(curl_handle, context->sockfd, flags,
        &running_handles);

    check_multi_info();
}

static void on_timeout(uv_timer_t* req)
{
    int running_handles;
    curl_multi_socket_action(curl_handle, CURL_SOCKET_TIMEOUT, 0,
        &running_handles);
    check_multi_info();
}

static int start_timeout(CURLM* multi, long timeout_ms, void* userp)
{
    if (timeout_ms < 0)
    {
        uv_timer_stop(&timeout);
    }
    else
    {
        if (timeout_ms == 0)
            timeout_ms = 1; /* 0 means directly call socket_action, but we'll do it
                               in a bit */
        uv_timer_start(&timeout, on_timeout, timeout_ms, 0);
    }
    return 0;
}

static int handle_socket(CURL* easy, curl_socket_t s, int action, void* userp,
    void* socketp)
{
    curl_context_t* curl_context;
    int events = 0;

    switch (action)
    {
    case CURL_POLL_IN:
    case CURL_POLL_OUT:
    case CURL_POLL_INOUT:
        curl_context = socketp ? (curl_context_t*)socketp : create_curl_context(s);

        curl_multi_assign(curl_handle, s, (void*)curl_context);

        if (action != CURL_POLL_IN)
            events |= UV_WRITABLE;
        if (action != CURL_POLL_OUT)
            events |= UV_READABLE;

        uv_poll_start(&curl_context->poll_handle, events, curl_perform);
        break;
    case CURL_POLL_REMOVE:
        if (socketp)
        {
            uv_poll_stop(&((curl_context_t*)socketp)->poll_handle);
            destroy_curl_context((curl_context_t*)socketp);
            curl_multi_assign(curl_handle, s, NULL);
        }
        break;
    default:
        abort();
    }

    return 0;
}

int main(int argc, char** argv)
{
    loop = uv_default_loop();

    if (argc <= 1)
        return 0;

    if (curl_global_init(CURL_GLOBAL_ALL))
    {
        fprintf(stderr, "Could not init curl\n");
        return 1;
    }

    uv_timer_init(loop, &timeout);

    curl_handle = curl_multi_init();
    curl_multi_setopt(curl_handle, CURLMOPT_SOCKETFUNCTION, handle_socket);
    curl_multi_setopt(curl_handle, CURLMOPT_TIMERFUNCTION, start_timeout);

    while (argc-- > 1)
    {
        add_download(argv[argc], argc);
    }

    uv_run(loop, UV_RUN_DEFAULT);
    curl_multi_cleanup(curl_handle);

    return 0;
}